Fix test risk_unit failing due to {raster} API change.

DESCRIPTION

 Package: mapMCDA
 Title: Produce an epidemiological risk map by weighting multiple risk
         factors
-Version: 0.4.17
+Version: 0.4.18
 Date: 2020-04-11
 Authors@R: c( person("Andrea", "Apolloni", email =
         "andrea.apolloni@cirad.fr", role = c("ctb"), comment = "Animal

tests/testthat/test-risk_unit.R

@@ -77,7 +77,7 @@ test_that("Missing CRS in epidemiological units", {
 
 
 test_that("Polygons not covering any raster-cell center", {
-  epi_ext <- raster::bind(raster::shift(epiunits[1], x = -5), epiunits)
+  epi_ext <- raster::bind(raster::shift(epiunits[1], dx = -5), epiunits)
   # plot(r)
   # plot(epi_ext, add = TRUE)